Respiratory protection devices commonly include a mask body and one or more filter cartridges that are attached to the mask body. The mask body is worn on a person's face, over the nose and mouth, and may include portions that cover the head, neck, or other body parts, in some cases. Clean air is made available to a wearer after passing through filter media disposed in the filter cartridge. In negative pressure respiratory protection devices, air is drawn through a filter cartridge by a negative pressure generated by a wearer during inhalation. Air from the external environment passes through the filter medium and enters an interior space of the mask body where it may be inhaled by the wearer.
In order to effectively deliver breathable air to a wearer, respiratory protection devices desirably provide an adequate seal to prevent unfiltered air from entering the mask. Various techniques have been proposed for testing the integrity of a seal provided by a respiratory protection device. In a positive pressure test, an exhalation valve of the respiratory protection device is blocked while the wearer exhales into the mask. An adequate seal may be signaled by an increased internal pressure due to the inability of air within the mask to escape through an exhalation valve if a leak is not present. Alternatively, negative pressure tests have been proposed in which a filter cartridge port is blocked while a wearer inhales while wearing the mask. An adequate seal may be signaled by a reduced internal pressure due to the inability of air to enter the mask if a leak is not present.